This invention relates generally to systems for recording signals on motion picture film, and, more particularly, to systems for recording a digital signal on such film while it is being intermittently advanced by a motion picture camera.
Motion picture film editing normally requires the accurate synchronization of motion picture film with an accompanying sound recording. The film can come from several different cameras operating simultaneously, and the sound recording can include a number of tracks for dialogue, music and appropriate sound effects. It is ordinarily essential that all of the film and sound tracks be arranged in precise synchronization with each other.
Synchronization is relatively easy when editing video tape, as contrasted with motion picture film, because a time code signal can be recorded in a separate time code channel adjacent an edge of the tape. Knowing the exact time at which a particular video frame was recorded makes it relatively easy to synchronize it with other video and audio tapes that record similar time code signals.
Editing motion picture film, on the other hand, has generally been more difficult, because devices have not been available for recording such time code signals on the film. Generally, the film has been synchronized with the various sound tracks by means of a clapstick and its resulting sharp noise. It is believed that one reason such time code signals have not been recorded on motion picture film is that the precise times at which the intermittent frame advancement begins and ends are somewhat variable. Although the magnitude of this variability is typically less than about one percent, this is nevertheless considered to be significant.
It has generally been thought to be impractical to record a continuous digital time code on the film, such as the conventional time code specified by the Society of Motion Picture and Television Engineers (SMPTE), which includes 64 timing and user bits and 16 synchronization bits for each picture frame. This is because such a recording might result in the loss of bits at the beginning and ending of each recording sequence caused by uncertainties in the specific times at which the intermittent frame advancement begins and ends. A conventional SMPTE time code reader therefore could not properly decode the bits to determine the timing of the corresponding picture frames and to determine other user information included in each 80-bit word.
It should therefore be appreciated that there is a need for a system that can record a digital signal such as an SMPTE time code on motion picture film such that the recorded signal can be decoded by a conventional time code reader even though the first and last bits associated with each picture frame might be missing or otherwise defective. The present invention fulfills this need.